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Terahertz waves emitted from an optical fiber
Yi, Minwoo,Lee, Kanghee,Lim, Jongseok,Hong, Youngbin,Jho, Young-Dahl,Ahn, Jaewook The Optical Society 2010 Optics express Vol.18 No.13
<P>We report a simple method of creating terahertz waves by applying the photo-Dember effect in a (100)-oriented InAs film coated onto the 45-degree wedged-end facet of an optical fiber. The terahertz waves are generated by infrared pulses guided through the optical fiber which is nearly in contact with a sample and then measured by a conventional photo-conductive antenna detector. Using this alignment-free terahertz source, we performed proof-of-principle experiments of terahertz time-domain spectroscopy and near-field terahertz microscopy. We obtained a bandwidth of 2 THz and 180-microm spatial resolution. Using this method, the THz imaging resolution is expected to be reduced to the size of the optical fiber core. Applications of this device can be extended to sub-wavelength terahertz spectroscopic imaging, miniaturized terahertz system design, and remote sensing.</P>
Combined Effect of Carrier Localization and Polarity in InxGa1-xN/GaN Quantum Wells.
Hwang, Hyeong-Yong,Choi, Sang-Bae,Jeong, Hoonill,Lee, Dong-Seon,Jho, Young-Dahl American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.8
<P>The influence of carrier localization and polarization-induced electric fields on the spectral variation of photoluminescence was comparatively studied in polar and semipolar InxGa1-x N/GaN strained quantum wells embedded in p-i-n diodes. Two representative structures with x = 0.16 for polar (0001) diodes and potential fluctuations for semipolar diodes grown along (1122) direction have been investigated with a reverse bias up to -4 V. From the s-shaped spectral shift as a function of temperature, the existence of single and triple localization traps was confirmed in polar and semipolar diodes. Within our bias range, we observed the monotonic blueshift with reverse bias in the polar sample, indicating that the carriers are laterally localized and thus influenced by the vertical piezoelectric fields. In clear contrast, the semipolar sample showed the blueshift of localized states only at low temperatures, while the deepest localization features were found at the highest available temperatures, overriding the influence of thermal activation and polarization fields.</P>
Directional Terahertz Radiation from GalnP Lateral Superlattice.
Yim, Jong-Hyuk,Song, Kyoung-Jin,Park, Kwang-Wook,Kang, Seok-Jin,Lee, Yong-Tak,Jho, Young-Dahl American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.7
<P>We devised directionally controllable THz emission sources based on lateral composition modulation (LCM) structures. LCM structures were composed of In-rich Ga0.47In0.53P and Ga-rich Ga0.51In0.49P layers whose period was in quantum scale of ~`5 nm. The inherent type II band alignment in these structures leads to electron-hole (e-h) separation and plays a key role in generating later- ally polarized dipole ensembles, thus concomitantly emitting enhanced transmissive THz waves as compared to bulk sample. On the other hand, in lateral geometry, changes in THz fields between LCM and bulk structures turned out to negligible since the vertical electronic diffusion was allowed in both samples.</P>
Polarized Terahertz Waves Emitted from In0.2Ga0.8As Nanowires.
Yim, Jong-Hyuk,Irfan, Muhammad,Song, Kyoung-Jin,Lee, Eun-Hye,Song, Jin-Dong,Jho, Young-Dahl American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.8
<P>We investigate the polarizability of terahertz (THz) waves emitted from undoped In0.2Ga0.8As nanowires (NWs). THz emission amplitude shows strong enhancement in vertically aligned NWs compared to less-aligned NWs. In particular, polarized THz waves are clearly demonstrated in aligned NWs via a drastic variation of amplitudes as a function of the axis angle in polarization-sensitive photoconductive antenna. In addition, phase reversal between aligned and less-aligned NWs substantiates the geometrical dependence of electronic diffusion in generating the transient THz electric fields.</P>